Save on energy year-round without blocking the sun's rays. The AirSkirts™ AirLight™ Skylight Insulator lets the sunshine in while preventing energy from escaping through your thin skylight cover. This inflatable insulator fits in your standard sized skylight (just select the correct size) and is made of a durable, clear PVC material that stays in place without any kind of adhesive, using only air pressure to keep it in place. Our standard 14"x14" (interior 13.5") is the most common size found in RVs, and will fit in most skylights and vents at this size. To be sure, measure the inside of your skylight or vent and verify that it's about 13.5" and you have at least 2 inches of depth. Our Airstream models are made for Airstream skylights but may fit some other RVs as well. The 19"x19" is for the large square skylight and the 21"x14.25" is for the rectangular skylight often found in the hallway.